1. Field of the Invention
The present invention relates to a method of and an apparatus for producing an additional print by exposing photographic paper on the basis of image data relative to a printed sheet of photographic paper.
2. Description of the Related Art
In a typical photograph printing apparatus, light emitted from a light source and transmitted through an original-image film is projected onto photographic paper by a lens unit and thus the photographic paper is exposed to an image on the film. Printing apparatus of the type that is applied to the printing of color photographs are arranged such that light rays emitted from a light source illuminate an original-image film via a light control filter device constituted by color compensating filters for yellow (Y), magenta (M) and cyan (C).
In such a printing apparatus, image-density sensors constituted by photosensitive elements such as photodiodes are interposed between the original-image film and the lens unit for detecting image density data relative to the film.
The image density data is supplied to an exposure controller, in which arithmetic operations upon the amount of exposure relative to each color are performed by the following equation so as to enable each photograph to be printed at an optimum exposure value corresponding to the density of each image formed on the original-image film. This is based on a known Evans' theorem. EQU logE.sub.i =logE.sub.Ni +C.sub.j (D.sub.Nj -D.sub.NNj) (1)
where
E: amount of exposure relative to the original-image film; PA0 E.sub.N : amount of exposure relative to a normal original-image film; PA0 C: correction factor relative to the density of the original-image film; PA0 D.sub.N : LATD of the original-image film; PA0 D.sub.NN : LATD of the normal original-image film; PA0 i: one of red, green and blue; and PA0 j: one of Y, M and C.
However, in actual printing, the amount of exposure calculated from the above equation (1) may be further corrected on the basis of a correction value relative to a specific image pattern. This correction is commonly performed by a skilled operator in order to prevent color and density from being imperfectly reproduced owing to a color-philia or density-philia.
In a case where a customer requests that a negative film be developed and at the same time an image be printed from each frame of the film on a sheet of photographic paper of the same size, the aforesaid printing apparatus can be used to produce initial prints without any difficulties. Thereafter, the customer may request that additional prints be produced from the same film. In this case, however, if reprinting is performed on the basis of the LATD of the original-image film of the customer, various problems are encountered. For example, even if the same printing and developing apparatus used for the initial printing are employed for the additional printing, variations occur in the operating state of the light source or the state of a developer. Therefore, the finish of additional prints is likely to differ from that of the initial prints and this constitutes one cause of complaints from consumers. In a particular case where a photograph is printed from a film having an image with an imperfect color balance, the operator makes more or less subjective corrections on the basis of his visual checking as described previously. Therefore, the same corrections as those of the initial prints are not necessarily performed for the additional printing, and this constitutes another cause of complaints from consumers.